This invention relates to brushless D.C. motors fabricated using superconductive materials and, more particularly, to such a motor in which the rotor temperature is controllable to a temperature below a critical temperature, while a stator winding is energized thereby to trap flux within the rotor portion of the motor so the rotor acts as a permanent magnet.
Trapping flux in a superconductor coil or in a bulk material can produce a relatively high energy "permanent magnet". As the flux trapping capability of high temperature superconducting (HTSC) materials improves, and difficulties in fabricating high current conductors diminish, there will be an increased number of motor applications that will benefit from such materials. The HTSC materials referred to include the families of ceramic based materials currently being developed. The high temperature referred to is a temperature above that of liquid helium (He) which is 4.2 degrees Kelvin (K). One advantage with these new type motors is their substantially lower weight and smaller size for a given power rating as compared to conventional motors. Theoretically, magnets made of HTSC materials will have five-to-ten times higher energy than magnets currently in use, for example, those made of rare earth. HTSC coils or the bulk material used in the new motors will need to be "charged" or magnetized just as conventional permanent magnets must be. Also, the rotor can be magnetized to one level for one application, and to a different level for the next.